Energy Sciences

Chiroptical properties in metal halide perovskites typically arise from asymmetric crystal structures induced by chiral organic molecules during synthesis or chiral additives. However, the synthesis of two-dimensional chiral halide perovskites with sufficiently high dissymmetry factors for practical applications remains challenging. Herein, we present a two-step ionic gel-mediated nucleation and recrystallization reaction, enabling the synthesis of nanostructured chiral halide perovskite films exhibiting large intrinsic circular dichroism dissymmetry factors (gCD) up to 10−2. The ionic gel mediates the reaction between lead(II) iodide (PbI2) and R/S-methylbenzylammonium iodide (R/S-MBAI), to facilitate the formation of higher-order iodoplumbate PbI3- and oligomeric Pb-I-MBA species, which recrystallize during heat treatment as anisotropic nanostructures without preferential orientation. Ionic gel-mediated films exhibit a very pronounced peak splitting originating from a well-defined exciton fine structure and narrow photoluminescence linewidth. This is indicative of the presence of electron-hole exchange interactions and minimized structural disorder in the material leading to significantly amplified chiroptical response. This work demonstrates a synthesis route for nanostructured chiral MBA2PbI4 films, whose unique structural feature with reduced crystalline imperfection enables amplified circular dichroism and gCD response.

Effective interfacial passivation is essential for achieving high-performance perovskite photovoltaics. 2D/3D heterostructures are a widely adopted strategy for defect passivation and band alignment regulation. Despite recent progress, achieving favorable interfacial energetics and comprehensively suppressing nonradiative recombination at both surfaces and grain boundaries continues to be an active area of investigation. We introduce a coassembled 2D architecture in which long-chain ligands are complemented by a minority component of short-chain ligands to form a mixed-ligand passivation layer. Such a coassembled structure promotes preferentially phase-pure, n = 2, 2D layer formation, resulting in an energetically favorable band alignment that enhances charge extraction. In addition, this coassembly facilitates effective passivation of interfacial defects at both surfaces and grain boundaries, leading to suppressed nonradiative recombination. As a consequence, these interfacial improvements increase carrier lifetimes and enhance the fill factor and open-circuit voltage of the device, yielding a higher power-conversion efficiency.

Effective water and thermal management are crucial for maximizing the performance of proton exchange membrane fuel cells (PEMFCs). This study presents a robust non-isothermal model that integrates two-phase flow, species transport, and heat and mass transfer phenomena to investigate water generation, accumulation, and permeation mechanisms within the gas diffusion layer (GDL) of PEMFCs. Utilizing X-ray computed tomography (XCT) reconstruction, a 2D structure of the Freudenberg GDL is generated. The model incorporates anisotropic thermal conductivity, distinguishes between in-plane and through-plane K IP K TP ratios, and demonstrates its importance to temperature distribution and subsequent condensation rate within the GDL. Additionally, our parametric analysis evaluates the effects of GDL thermal conductivity, current density, operating temperature, and pressure on water condensation and transport processes in PEMFCs. Key findings include the identification of distinct phases of condensation and transport within the porous medium under varying conditions: nucleation, growth, accumulation, and mobilization. Simulation results uncovered condensation regions within the GDL, demonstrating that temperature gradients, strongly influenced by anisotropic thermal conductivity, play a critical role in water generation and transport dynamics. The study further reveals that areas beneath the land in the GDL exhibit lower temperatures, leading to elevated condensation rates and larger droplet formation within those regions. Additionally, the interconnection of condensate droplets via wetting layers emphasizes the impact of temperature distribution on water movement. This study provides deeper insight into water vapor condensation and transport mechanisms within GDLs, informing the design and optimization of GDL structures for enhanced PEMFC performance.

Macromolecular crystallography has historically inferred models of internal crystal architecture from reciprocal-space measurements of Bragg reflections. Nevertheless, direct real-space visualization of crystallographic disorder remains elusive, particularly at the nanoscale. Using a 15-nanometer probe, here we apply both ambient-temperature and cryogenic four-dimensional scanning transmission electron microscopy (4D-STEM) to map the topography of coherently diffracting domains (CDDs) in lysozyme and myoglobin microcrystals at length scales 100 × finer than conventional X-ray and electron beams. Virtual dark-field images show that each Bragg peak arises from spatially distinct subvolumes representing smooth and continuous variations in local lattice orientation. Under sustained irradiation, protein CDDs undergo rearrangements spanning several micrometers of internal movement. Furthermore, pinpoint high-dose "impact crater" experiments reveal delocalized radiolytic damage propagating hundreds of nanometers from primary irradiation sites, behavior similar to small-molecule crystals but amplified in both rate and magnitude. Together, these results establish macromolecular microcrystals as dynamic assemblies whose internal architecture continuously reorganizes during irradiation, laying the foundation for realistic models of mosaicity directly informed by both real-space and reciprocal-space observations.

Autoencoder-transformer model applicable to both simulated and experimental XAS spectra is developed to predict the oxidation state of copper. X-ray absorption spectroscopy (XAS) and electron energy-loss spectroscopy (EELS) produce detailed information about oxidation state, bonding, and coordination, making them essential for quantitative studies of redox and structure in functional materials. However, high-throughput quantitative analysis of these spectra, especially for mixed valence materials, remains challenging as diverse experimental conditions introduce noise, misalignment, and broadening of the spectral features. We address this challenge by training a machine learning model consisting of an autoencoder to standardize the spectra and a transformer model to predict both Cu oxidation state and Bader charge directly from L-edge spectra. The model is trained on a large dataset of FEFF-simulated spectra, and its performance is evaluated on both simulated and experimental data. The results of the machine learning model exhibit accurate and transferable predictions across the domains of simulated and experimental spectra. These advances enable future quantitative analysis of Cu redox processes under in situ and operando conditions.

High-resolution scanning transmission electron microscopy (S/TEM) is an indispensable tool for characterizing the structure and properties of materials down to the atomic scale. Conventional S/TEM imaging, however, is limited by the phase problem, whereby the phase of the electron exit wave is lost upon detection. Recent advances in diffractive imaging and 4D-STEM have enabled a range of phase-retrieval techniques that computationally reconstruct the missing information encoded in the phase of the transmission function. These approaches offer improved dose efficiency and enhanced sensitivity to weakly scattering signals, extending quantitative imaging to beam-sensitive materials composed of light elements. In this work, we introduce the phase problem in electron microscopy and survey the diverse landscape of phase-retrieval techniques used in the field. Despite their many acronyms and algorithmic variations, these techniques share a common physical and mathematical foundation. We present a unified framework that connects these seemingly distinct methods, from parallax imaging and tilt-corrected bright-field (tcBF-STEM), to aberration-corrected bright-field (acBF-STEM), optimum bright-field (OBF-STEM) and single-sideband (SSB) ptychography, as well as first-moment integrated center of mass techniques (iCOM) and iterative ptychographic algorithms. Based on these insights, we discuss the opportunities and practical limitations of applying these methods across different materials systems, detector designs, and microscope configurations.Graphical abstractRepresentative electron microscopy configurations used for phase retrieval and diffractive imaging in S/TEM: (a) Zernike phase-contrast transmission electron microscopy (TEM), (b) small-convergence-angle four-dimensional scanning transmission electron microscopy (4D-STEM) for nanobeam-based phase reconstruction methods, and (c) large-convergence-angle 4D-STEM for ptychographic and related diffractive imaging techniques reviewed in this work.

The structural biology method of X-ray footprinting mass spectrometry (XFMS) is available at two national synchrotron beamlines in the USA: one at the Advanced Light Source (ALS) on the West Coast and the other at the National Synchrotron Light Source II on the East Coast. XFMS is a solution-state technique that utilizes oxidative modifications of proteins at micromolar concentrations in aqueous buffer to extract structural information. X-rays are employed to generate hydroxyl radicals in situ, which covalently modify specific protein side chains. These modifications are subsequently quantified using liquid chromatography and mass spectrometry. Ratiometric changes in modification levels between two protein states (e.g. with and without ligand) generate a relative solvent accessibility map of the protein pairs, which serves to reveal structural features. Up until recently, the XFMS capability was available as part of a shared program at the ALS without a dedicated beamline. In this article, we describe the commissioning of ALS beamline 3.3.1, dedicated to XFMS, including the installation of a new focusing mirror, the design and construction of a new endstation with automated sample handling and exposure capabilities, and the use of accurate empirical dose calculations using Gafchromic film. Finally, we showcase the new beamline capabilities using two protein systems.

Solute-intercalation-induced phase separation creates spatial heterogeneities in host materials, a phenomenon ubiquitous in batteries, hydrogen storage, and other energy devices. Despite many efforts, probing intercalation processes at the atomic scale has been a significant challenge. By utilizing liquid-phase transmission electron microscopy (TEM), we study hydrogen (de)intercalation in palladium nanocrystals as a model system and have achieved unprecedented atomic-resolution imaging of hydrogen intercalation wave dynamics. Our observations reveal that intercalation wave mechanisms, instead of shrinking-core mechanisms, prevail at ambient temperature for palladium nanocubes ranging from ∼60 nm down to ∼10 nm. Systematic image analysis uncovers the atomic evolution of the hydrogen intercalation wave, transitioning from nonplanar and inclined boundaries to those closely aligned with {100} planes. Our kinetic Monte Carlo simulations demonstrate that the observed intercalation wave dynamics correspond to sorption pathways minimizing the lattice mismatch strain at the phase boundary. Unveiling the atomic intercalation pathways holds profound implications for engineering intercalation-mediated devices and advancements in energy sciences.

Atomic structures of nanomaterials are inherently dynamic and continuously reshaped through interactions with chemical species and external stimuli. Such dynamics are further amplified as the size and dimensionality of nanomaterials decrease. Despite advances in analytical methods, it remains challenging to capture the structural dynamics of nanomaterials in reactive environments with both atomic spatial resolution and commensurate temporal resolution. Here, we directly visualize atomic-scale dynamics of gold (Au) nanocrystals in reactive liquid environments with millisecond-speed liquid-cell electron microscopy (EM) and deep-learning denoising. We uncover reversible fluctuations in the local crystallinity of Au nanocrystals dependent on the surrounding chemical environment. These transient fluctuations, driven by interactions at nanocrystal-liquid interfaces, critically influence the dissolution kinetics and grain boundary relaxation. By overcoming the spatiotemporal limitations in conventional liquid-cell EM, our findings provide insights into how transient nanoscale structures dictate the stability and reactivity of nanomaterials.

Balancing moisture and oxygen replicates inert crystallization dynamics in antisolvent-free halide perovskite processing under ambient conditions. Understanding crystallization in ambient environments is essential for scaling the fabrication of halide perovskite solar cells. Antisolvent-free perovskite deposition offers improved compatibility with high-throughput processing but introduces distinct crystallization dynamics relative to the more ubiquitous use of antisolvents in lab-scale perovskite fabrication. These dynamics are driven by interactions between solutes, solvent and the deposition environment. Using in situ wide-angle X-ray scattering during spin-coating and annealing, we demonstrate how relative humidity (RH) and oxygen, can be tuned to drive polytype evolution during ambient crystallization of formamidinium lead iodide to match that of inert synthesis and achieve comparable film and device quality. In an inert (N 2 ) environment, we find that perovskite films follow a well-established 2H → 3C phase transformation with a short period of coexistence of the 4H and 6H phase during heating. During crystallization in dry air (RH 0%), the added presence of oxygen leads to the dominance of 4H intermediate for an extended duration, establishing a 2H → 4H → 3C pathway. Introducing low humidity (RH 10%) suppresses the 4H phase to a short-lived intermediate above 100 °C, facilitating a more direct transition to the desired 3C phase and almost replicating the crystallization behavior observed under inert conditions. Interestingly, films crystallized under RH 10% show a lower onset temperature for the perovskite 3C phase than under N 2 . At higher humidity (RH 40%), the strong interaction of oxygen and moisture with iodoplumbates appears to stabilize higher order polytypes (4H and 6H). Devices fabricated under RH 10% achieve higher efficiency and enhanced stability compared to those produced under inert atmosphere. These findings provide mechanistic insight into crystallization pathways in different environments and provide a framework to transfer processes from inert to ambient conditions. The results highlight the critical role of controlled humidity in tuning antisolvent-free perovskite crystallization for scalable processing.